The present invention relates to a focused ion beam system by which a focused ion beam is applied onto a surface of a specimen, while scanning the surface of the specimen with the focused ion beam, and while spraying the surface of the specimen with gases, to thereby carrying out fine patterning.
Heretofore, in order to provide selectivity and increased sputtering rate in the etching process, the etching process is carried out while spraying a position on a surface of a specimen, which is being irradiated with a focused ion beam, with a local gas (commonly referring to as an assist gas). As for this assist gas, in order to provide the reactivity with a material of a specimen, a halogen series gas (for example, a chlorine gas) is mainly employed.
In addition, in order to focus the ion beam emitted from an ion source, there is provided a focusing lens (an electrostatic lens) including a condenser lens and an objective lens. Also, as for a material of each of the condenser lens and the objective lens, in terms of installation of those lenses in a vacuum and ease of processing of those lenses, a stainless steel material such as SUS304 is typically employed.
In the above-mentioned focused ion beam system, however, the etching assist gases react not only with the specimen, but also with focusing lens and the like made of a stainless steel material (i.e., the chemical etching occurs), and hence the surface of the focusing lens is roughened due to the chemical etching. In addition, the reactant is deposited on the surface of the focusing lens so that the irregularity of the surface of the focusing lens is increased. At this time, if applying a high voltage (several tens kV or so) to the focusing lens, then, there is provided the state in which the discharge is easy to be generated between the focusing lens and the earth.
If the discharge is generated during the processing, then the focused ion beam is applied to areas other than the predetermined area irradiated therewith, and this disables the desired processing and observation, respectively. In addition, a large amount of current is caused to flow through a control power source 13 due to the generation of the discharge so that the control power source 13 may be destroyed. Those are problems associated with the prior art for which a need arises to prevent undesired etching of and deposition onto the focusing lens of a system employing a focused ion beam.